1. Field of the Invention
This invention relates generally to cellular radio communication systems and, more particularly, to an RF filter architecture for receiving signals in the two cellular bands allocated for cellular radio transmission.
2. Description of Related Art
Recent agreements between service providers of cellular radio communications involve the desire to receive signals in a competitor""s designated frequency band in order to improve network performance. Specifically, one service provider would measure a mobile""s signal strength and determine the identification for a mobile which is not in the provider""s band, but may be on a cell boundary. If the mobile is at a cell boundary, a sector-to-sector or cell-to-cell handoff would become necessary. Since the mobile may be handed off to the service provider""s base station, this verification is necessary in determining if enough receive signal is present to allow adequate link performance.
The prior art regarding such a scenario would be to install two separate and distinct base station receiver front ends, one for each of the two allocated bands, A and B, to allow a xe2x80x9ccross-band locatexe2x80x9d functionality.
Accordingly, it is an object of the invention to provide an improvement in cellular radio receiver apparatus.
It is another object of the invention to provide a front-end architecture which supports simultaneous filtered reception of both cellular bands with a common set of receiver hardware.
It is still a further object of the invention to provide cellular radio receiver apparatus including filter architecture for supporting reception of cellular A and B bands of the cellular radio frequency spectrum.
The foregoing and other objects of the invention are achieved by a combination of signal circulators and bandpass filters which operate to selectively notch out sub-bands of the two cellular bands of the cellular radio transmission spectrum so that the sub-bands of both cellular bands can be directed to a radio capable of receiving either the A or B-band signals.
In its preferred embodiment, the invention is directed to an RF filter architecture in a cellular radio receiver for supporting two different cellular receive bands of the spectrum for cellular radio communications where each band includes at least two sub-bands, comprising: a first RF signal circulator having a plurality of signal ports including an input port for receiving an RF input signal and at least two output ports; a first bandpass filter having a first frequency bandpass characteristic and having a pair of signal ports including an input port and an output port, said input port being coupled to one of the two output ports of the first circulator; a second bandpass filter having a second frequency bandpass characteristic different from the first bandpass characteristic and having a pair of signal ports including an input port and an output port, the input port thereof being coupled to the other output port of the two output ports of the first circulator, the output port of the second bandpass filter providing a first output signal corresponding to one or more sub-bands of the two cellular receive bands, wherein said first circulator and said first bandpass filter operate to notch out frequencies within the first bandpass characteristic from the first output signal; a second RF signal circulator having a plurality of signal ports including an input port coupled to the output port of the first bandpass filter and at least two output ports, one of the output ports of the second circulator providing a second output signal corresponding to one or more sub-bands of the two cellular receive bands; and, a third bandpass filter having a third bandpass frequency characteristic different from the first and second bandpass characteristic and having a pair of signal ports including an input port and an output port, the input port thereof being coupled to the other of the output ports of the second RF circulator, the output port of the third bandpass filter providing a third output signal corresponding to one or more sub-bands of the two cellular receive bands, and wherein the second circulator and the third bandpass filter operate to notch out frequencies within the third bandpass characteristic from the second output signal and wherein the first and third output signals include the sub-bands of a first band of the two cellular receive bands such as the A-band and the second output signal includes sub-bands of a second band of the two cellular receive bands such as the B-band.
Further scope of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood, however, that the detailed description and specific examples, while providing the preferred embodiments of the invention, are provided by way of illustration only, since changes and modifications coming within the spirit and scope of the invention will become apparent to those skilled in the art from the detailed description.